ENH: Use preallocated buffers in Pop array methods

Change the behavior of the Pop "array" methods. Now,
if the input array is not null, the code would expect
that the array is properly allocated, i.e., its size
should match the size of the data read and it would
just fill in the given buffer.

Change-Id: Ic1936418d01380bd9d0efffeacebd4b8066b4a31
ENH: Support for VtkIdType & enhancements

This method adds support for serializing/deserializing arrays
of vtkIdType. Further, it modifies the implementation such that
the array is popped from the bytestream directly in to the
pointer of the vtkDataArray instance as opposed to a temporary
buffer.

Change-Id: If090808933a5e4563d232b2657995c643536342f
WIP: unstructured ghost zones

Change-Id: Idd9ce355f8070bbdf882cdb2350fdcbce2c4b845